This sled is of the Frankenstein variety – it is cobbled together from materials left over from other projects. I had just made a table saw sled but was disappointed in the amount of play in the runners. I was using the sled to make some small boxes, and it kept giving me inaccurate cuts that took way too much time to correct. I knew that if I wanted to complete these boxes and other projects to a higher standard, I was going to have to bite the bullet and sacrifice the sled to make a new sled. Once I came to that conclusion, I also wanted to incorporate some features I’ve seen in other sleds and this gave me the opportunity.
The bed is ¾” plywood that came from the door of a homemade cabinet I literally found in an alley. Sure, I should have bought some new plywood but this piece seemed nice and flat and the other great feature was that I already had it. For the runners, I used some maple that I bought years ago to make the top of my workbench. It was from a company that makes counter tops and butcher block and seems very stable. It started out at about an inch thick, so I planed it down to fit the slots of my table saw. Once it was the right thickness, I ripped two runners and set the rest of the piece aside to use for runners for future sleds and jigs.
I used a piece of this maple for the fence of my now-dead sled. It wasn’t perfectly straight and even had a slight bit of flex in it. I salvaged that piece for my new sled and glued another piece of maple to it, making it almost 2 inches thick (that should resist flexing!). I used a hand plane to make one side flat, then my power planer to go to final thickness. For the back fence, I didn’t have any more of this maple, so I used a piece of butternut. Now, butternut isn’t the hardest stuff out there but it was a good board and I had it on hand (see title). It’s over an inch thick, so I think it should do its job just fine.
To install the runners, I used the method where you insert the runners in the slots (propped up a little) and use the table saw’s fence to make sure the bed was square on the table. I added a thin line of glue to both runners, then set the bed on top of them. I grabbed the heaviest stuff I could find to put on top to make sure the bed came into good contact (that turned out to be my grinder, plus a few drills, etc.). After that dried, I moved the bed back and forth and there was no play at all. I then countersunk and added screws to the runners from the bottom side up. Everything was going great until I decided to cut off the ends of the runners that protruded out the back. They must have been somewhat warped and were keeping the runners tight in the slots. When I cut them off, it relieved that tension and now there was play in the runners. I was crest fallen for a moment. I had already gone to all this effort and had glued the runners on. I measured that the play was about 8/1000s. I was thinking about drastic measures, including routing a rabbet on the runners and adding a new piece of material to get a tighter fit. I’m glad I didn’t do that. Instead, I put on a piece of the metal-sided tape that you use in an HVAC system. I also added lots of wax. The runners were very, very snug and I couldn’t move them easily. After working them back and forth many times, they started to loosen up. I added the fence and started making cuts to test for square. The results were horrible. It was 1/32” off over about 6 inches. Then I re-watched a Wood Whisperer video (link below) on making a sled in which his runners were too tight. He used a card scrapper to take a tiny bit off the sides of the runners where they were binding. That worked like a charm. The reason my cut was so out of square is that I was lunging the sled during the cuts, sending everything out of whack (that’s a technical term). That wasn’t terribly safe either.
With the runners now moving freely and with no side to side play, I squared the fence and did the WoodWhisperer’s 5-cut process. The result was great. I was off less than .012”. Using Marc’s math, you divide this measurement by 4 to get the actual error. I calculated that I was about 3/1000” off over 36”. One thousandth per foot? That’s fine by me.
Now for the fancy stuff. I know that the kerf on a table saw sled can get chewed up with lots of use, so I looked to Lumberjock Kent Shepherd example of a replaceable insert. I routed a ¼”-deep channel in the bed. I should have used ¼” plywood, but I didn’t have any on hand (again, see title), so I used some cherry left over from another project. Once I routed out the channel (about 3 inches wide), I milled the cherry to fit it. I went ahead and made two more inserts using the same saw set up so I’ve got those when I need them. I fitted it very snugly in the channel and I also used three screws on both sides in a staggered pattern to resist splitting the cherry. I was very, very careful in placing the screws closest to the blade to make sure they didn’t come into contact with the blade. You’ll see on the back fence that I cut a little relief so that the insert could be removed and replaced. The other end nestles snugly under the fence. The other part that gets chewed up is the kerf in the main fence, so I also made a replaceable insert for that too. To round it out, I installed a track on the fence for use with stop blocks, etc.
I’m really glad I stuck with it and finished this sled. The next thing I’m going to do is add a safety block behind the blade. Then I’m going to make some accessories for it, such as some stop blocks, some hold-downs, a tenon jig and a miter jig. As long as I’m accessorizing, maybe I’ll add some throw pillows.
-- Mitch, http://furnitude.blogspot.com